interface ComputerAverage{
    public  double average(double a,double b);

}
class A implements ComputerAverage{
    public double average(double a,double b){
        double aver = 0;
        aver = (a+b)/2;
        return  aver;
    }
}
class  B implements ComputerAverage{
    @Override
    public double average(double a, double b) {
        double aver =0;
        aver = Math.sqrt(a*b);
        return aver;

    }
}

public class e6_4 {
    public static void main(String[] args) {
        ComputerAverage computer;
        double a=11.23,b=22.78;
        computer = new A();
        double result = computer.average(a,b);
        System.out.printf("%5.2f和%5.2f的算术平均值:%5.2f\n",a,b,result);
        computer = new B();
        result = computer.average(a,b);
        System.out.printf("%5.2f和%5.2f的算术平均值:%5.2f\n",a,b,result);
        }
    }


